Process of preparing oxymethylene copolymers



United States Patent 3,544,521 PROCESS OF PREPARING OXYMETHYLENECOPOLYMERS Calvin N. Wolf, Princeton, N.J., assignor to EthylCorporation, New York, N.Y., a corporation of Virginia No Drawing.Continuation of application Ser. No. 220,062, Aug. 28, 1962. Thisapplication Feb. 21, 1967, Ser. No. 617,712

Int. Cl. C08g 1/18 U.S. Cl. 260-73 8 Claims ABSTRACT OF THE DISCLOSUREPreparation of a linear thermoplastic oxymethylene copolymer of 2.formaldehyde and a dihydrocarbyl ester of a dicarboxylic acid. Thediester of the dicarboxylic acid has a formula wherein R and R aremonovalent, hydrocarbon radicals having up to about 32 carbon atoms eachof which may, for example, be an alkyl, cycloalkyl, aryl or alkarylgroup. R is a divalent hydrocarbon radical having from about 1 to about12 carbon atoms and is an alkylene, arylene or cycloalkylene group.These polymers exhibit the desired charcteristics of polyoxymethylene inthat they are tough, resilient, resistant to thermal degradation andhave enhanced resistance to degradation when in contact with stronglyalkaline substances.

This application is a continuation of my copending application Ser. No.220,062, filed Aug. 28, 1962, for Composition of Matter, now abandoned.

This invention relates to novel and useful high molecular weight, highmelting interpolymers composed primarily of formaldehyde. This inventionfurther relates to processes for producing these novel interpolymers.

In the past, Staudinger, in Die Hochmolecularen Organischen Verbindunger(1932), set forth a process of polymerizing formaldehyde. Theformaldehyde polymers obtained by this process, when aged in air at 105C. re sulted in degradation or unzipping to monomeric formaldehyde.McDonald, in U.S. Pat. 2,768,994, described a new polymerization processwhereby high molecular weight formaldehyde homopolymers could beproduced which were tough and possessed a higher degree of thermalstability than the low molecular weight polymers of Staudinger. Thepolymer produced by McDonald, which exhibited excellent properties atlow temperatures also tended to degrade or unzip at temperatures atwhich the polymer would be worked, e.g., molded. Thus, in the moldingoperations which require high temperatures, it was found thatpolyformaldehyde would degrade rendering the polymer relatively uselessfor this necessary operation.

Many methods have been attempted to stabilize the high molecular weightformaldehyde homopolymers. A typical method employed utilized thecompounding with the formaldehyde polymer of stabilizers such ashydrazines (U.S. Pat. 2,810,708), phenols (U.S. Pat. 2,871,220), ureas,thioureas (U.S. Pat. 2,893,972), amines (U.S. Pats. 2,920,059, and2,936,298), and benzophenones (Australian Pat. 230,163). The art hastaught that these stabilizers are compounded into the polymer after thepolym- Patented Dec. 1, 1970 erization process. These stabilizers seemto prevent to some extent oxidation, thermal deterioration and photodegradation, however, degradation is still experienced at hightemperatures in the presence of air.

Other methods employed to prevent the unzipping of the polyformaldehydeare the end capping of the free hydroxyl groups on the chain ends of thepolymer as set forth, for example, in U.S. Pat. 2,964,500. This endcapping procedure is successful to a certain degree but total success isnot experienced since these end capped polymers also degrade at hightemperatures or in the presence of caustic or other strongly alkalinesubstances.

Another method of stabilization includes the essentially completeremoval of the polymerization catalyst from the polymer since it isbelieved that the presence of the polymerization catalyst causesdegradation or unzipping (U.S. Pat. 2,989,509). Combinations of theforegoing have also been utilized (Austrialian Pat. 229,481).Copolymerization of formaldehyde with alkylene carbonates as set forthin U.S. Pat. 3,012,990, has also been achieved in the attempt to producea thermally stable polymer.

Another method of preventing degradation or unzipping of theformaldehyde polymer has been the copolymerization of trioxane withcyclic ethers such as ethylene oxide to produce a polymer havingadjacent carbon atoms breaking the alternating oxygen to carbon linkage(U.S. Pat. 3,027,352).

It is therefore an object of the present invention to provide novelinterpolymers which are stable and resistant to oxidative deteration,thermal deterioration, and caustic degradation. It is a further objectof the present invention to provide new, novel polymers which are tough,strong, flexible, and elastic in nature. It is a still further object ofthe present invention to provide novel interpolymers of formaldehyde ortrioxane and a dihydrocarbyl ester of a dicarboxylic acid which have thequalities outlined hereinabove. It is a further object of the presentinvention to provide a process for producing novel polymers havingthermal and oxidative stability and exhibiting properties of toughness,strength, and resilience. A particular object of this invention is toprovide novel high molecular weight thermally stable formaldehyde-esterpolymers which have substantially greater resistance to causticdegradation than high molecular weight polyoxymethylene homopolymers.Other objects of the invention will be apparent from the ensuingdescription.

It has now been found that the above and other objects are accomplishedby the provision of a polymer of a formaldehyde and a dihydrocarbylester of a dicarboxylic acid. The dihydrocarbyl ester of thedicarboxylic acid generally has the formula:

0 moJi-a-ii-om wherein R and R are organo groups having up to about 32carbon atoms each of which can be alkyl, cycloalkyl, aryl, and alkarylgroups; R is a divalent hydrocarbon radical having from about 1 to about12 carbon atoms and is for example an alkylene, arylene or cycloalkylenegroup. The preferred esters are those in which R, and R have from about1 to about 18 carbon atoms each and R has from about 2 to about 8 carbonatoms, since thermally stable polymers are obtained when theseparticular esters are employed and chemically combined in the polymerchain. Thus, a few typical examples of these esters are diethyl maleate,dibutyl succinate, diallyl phthalate and the like. Generally the amountof ester monomer present in the polymers of this invention ranges fromabout 0.1 mole percent, to about 20 mole percent based on the weight ofthe polymer. The preferred amount of diester monomer present in thepolymer generally ranges from about .5 to about mole percent. Excellentpolymers are obtained especially when the preferred mole percentage ofdiester, monomer is employed. These polymers exhibit the desirablecharacteristics of polyoxymethylene in that they are tough, resilient,and resistant to thermal degradation. But unlike the high molecularweight homopolymers of polyoxymethylene, the present novel interpolymershave enhanced resistance to degradation when in contact with stronglyalkaline substances.

A formula which shows the probable theoretical molecular structure ofthe novel polymers of this invention wherein R is a dihydrocarbyl estergroup, M is an integer representing the total number of polyoxymethyleneunits in the polymer and N is a smaller integer representing the totalnumber of dihydrocarbyl ester groups chemically combined intermittentlyat random throughout the polyoxymethylene structure. Therefore N is fromabout 0.1 to about 20 percent of M.

The novel interpolymers of this invention have high molecular weightsand high melting points. The molecular weights of these novelinterpolymers generally range from, about 5,000 to about 200,000.However, the preferred molecular weights range from about 10,000 toabout 150,000 since the copolymers obtained within this range are moreeasily adapted for the ultimate end use, e.g., molding, drawing fibers,and the like. The molecular weight ranges are a direct function of theinherent viscosity. Thus, inherent viscosities ranging from about 0.3 toabout 5.0 are desirable in the polymers of this invention. The mostpreferred inherent viscosities range from about 0.5 to 3.0 since theseviscosities correspond to polymers within the preferred molecular weightrange. The inherent viscosity is preferably measured at 0.5 percent byweight in p-chlorophenol containing 2 percent of alpha-pinene at 60 C.The melting point (polymer melt temperature) ranges of the novelinterpolymers of this invention generally range from 140 C. up to about190 C. The most preferred melt point range for these copolymers is fromabout 150 C. up to about 185 C. since polymers within this melting pointrange generally exhibit superior molding characteristics.

An important feature of the novel interpolymers of the present inventionis the fact that severe thermal degradation or unzipping is notexperienced at the elevated temperatures required for moldingoperations. Coupled with this advantageous feature is the fact thatthese novel interpolymers exhibit properties of toughness, resilience,strength, and flexibility. Still another important feature of theinterpolymers of this invention is their resistance to degradation inthe presence of strong caustic solutions. Formaldehyde homopolymers inthe past have rapidly decomposed into monomeric formaldehyde upon beingtreated with a strongly alkaline solution. This disadvantage is notexperienced to an appreciable extent with the present novelinterpolymers and in many cases the only modification experienced whenthese are treated with caustic solution is the elimination of theterminal hemiacetal groups from the polymer. This is advantageous inthat the remaining polymer is resistant to the action of acids, alkalis,heat, oxidation, and aging. Thus, many of the disadvantages experiencedin the prior art formaldehyde polymers have now been overcome, or atleast significantly reduced.

The term polymer as used in this invention, may be 4 further defined aspolymers containing 2 or more monomers as defined above. Thus,interpolymers such as copolymers, terpolymers, tetrapolymers, and thelike are all within the ambit of this invention.

The novel polymers of this invention are not to be confused with certainmaterials produced heretofore. Typical of these difierent materials arethe compositions described in British Pat. 863,176 according to whichesters such as diallyl maleate are employed as crosslinking agents inpolyoxymethylene. The esters form crosslinking bridges between thepolyoxymethylene chains. These cross-linked polymers are described asbeing insoluble or at least having decreased solubility and an increasedpolymer softening temperature, i.e., higher polymer melt temperature.

In sharp contrast to the prior art cross-linked polymers, the polymersof this invention retain the beneficial properties of truepolyoxymethylene. The novel polymers of this invention arev soluble incertain solvents and have a polymer melt temperature approximating thatof the pure polyoxymethylene. In addition to the retention of thesebeneficial properties the polymers of the present invention haveincreased thermal stability.

A further embodiment of the present invention relates to a process forproducing the novel polymers. The novel polymers of this invention areproduced by polymerizing any reactive form of formaldehyde which isessentially anhydrous with one or more dihydrocarbyl esters of adicarboxylic acid as described hereinabove. This polymerization processis conducted in the presence of a cata lyst, the nature of which largelydepends on the type of formaldehyde being utilized. Thus, when trioxaneis being copolymerized with one or more diesters, generally a Lewis acidis employed. However, heterogeneous catalysts, e.g., silicia alumina,are also very active in the copolymerization process. Other catalystssuch as Lewis bases are generally preferred when essentially anhydrousgaseous monomeric formaldehyde is being employed in the copolymerizationreaction.

The novel process of the present invention can be conducted utilizing awide variety of polymerization techniques, e.g., bulk polymerization,solution polymerization, vapor polymerization and like procedures.

Bulk polymerization is achieved by mixing any reactive form offormaldehyde such as trioxane with a catalyst and the desired diestermonomer(s). Thereafter the reaction mixture is heated to a temperatureof from about 60 C. to about C. for a period of time sufficient tocopolymerize the reaction mixture. This reaction time generally variesfrom a matter of a few seconds to one day, a period ranging from aboutthree minutes to twelve hours generally being sufficient. The resultingpolymer obtained may then be ground up and/or subjected to otherstabilization procedures, e.g., compounded with stabilizers and thelike.

Solution polymerization generally comprises contacting a formaldehydesource such as trioxane with a catalyst and the desired diesters in aninert solvent such as a liquid hydrocarbon at a temperature ranging fromabout -90 C. up to about 200 C. The reaction is generally conducted at apressure ranging from about atmospheric up to about 15 atmospheres. Thereaction mass is stirred and heated for a time sufficient to obtain thedesired molecular weight after which the copolymer product is extractedand allowed to dry. Again, subsequent treatments used in the art forimproving the properties may be used as desired.

The inert solvents which may be employed in the solution polymerizationprocess are any solvents which are inert to the reactants. 'Ihus, liquidhydrocarbons (paraf- -fins, cycloparaflins, aromatics, or mixtures ofthese), glycol ethers, monoethers, (dialkyl ethers, dicycloalkyl ethers,diaryl ethers, diaralkyl ethers or mixed ethers in which the organicgroups are taken from diiferent classes, vis, alkyl, cycloalkyl, aryl,and aralkyl groups). Saturated hydrocarbons, and the like may beemployed. Typical of the solvents are hydrocarbons such as hexane,heptane, octane, cyclohexane, methyl cyclohexane, benzene, toluene,xylene; petroleum distillates such as naphtha, kerosene, gasoline;halogenated hydrocarbon compounds such as carbon tetrachloride, ethylenedibromide, methylene chloride; glycol ethers, such as the dimethyl etherof diethylene glycol, the diethyl ether of diethylene glycol; monoetherssuch as diethyl ether, dibutyl ether, dicyclohexyl ether, dibenzylether, diphenyl ether, methylphenyl ether, and the like.

Vapor polymerization comprises contacting in a reaction zone the vaporsof a formaldehyde source such as trioxane and the desired diestermonomer(s) in the aerosol state in the presence of a catalyst attemperatures ranging from about 20 C. up to about 200 C. The pressure atwhich the vapor polymerization processes can be conducted generallyranges from atmospheric up to about 200 atmospheres. The polymer maythen be withdrawn as it is formed in the reaction chamber. Thereafteroptimum workup and/or stabilization procedures may be utilized.

The processes as outlined above are capable of being adapted to acontinuous process, a batch process, or semi batch operation; forexample, where a vapor polymerization reaction is being conducted it mayreadily be converted to a continuous process by merely adding thereactants and the catalyst to the reaction zone while recovering theinterpolymer as soon as it is formed. An excellent example of a batchprocess is the bulk polymerization of a formaldehyde source such astrioxane with a diester after which the desired polymer may then berecovered.

Generally it is preferred to employ an essentially anhydrous inertatmosphere over the reaction mass particularly when bulk polymerizationtechniques are being employed. However, an inert atmosphere may beemployed in other polymerization processes such as solutionpolymerization and vapor polymerization. Typical of the inert gaseswhich may be employed are nitrogen, argon, krypton, neon, helium, andthe like. Certain saturated paraffinic hydrocarbons may also be employedas the inert atmosphere where the hydrocarbons are inert to the reactionmass. Examples of paraffinic hydrocarbons which may be employed aremethane, ethane, propane, and the like.

The formaldehyde employed as stated herein above can be any reactiveform of formaldehyde in the essentially anhydrous state. Monomericformaldehyde and trioxane are the best known reactive anhydrous formswhich may be used. Monomeric formaldehyde can be produced by any of thegeneral prior art methods such as is set forth by Walker inFormaldehyde, A.C.S., Monograph Series No. 98 (1944). Typical methodsemployed to obtain monomeric formaldehyde are pyrolyzingparaformaldehyde, polyoxymethylene or other polymeric forms offormaldehyde. However, it is preferred in this invention to employtrioxane since it is easier to handle especially in bulk polymerizationprocesses. On the other hand, in vapor polymerization processes it ismore desirable to employ gaseous anhydrous monomeric formaldehyde sincethis compound is more easily vaporized.

Typical of the Lewis acids which are employed as catalysts in theprocesses of this invention are inorganic halides, particularly theinorganic fluorides, inorganic fluorides complexed with ethers andamines, methyl alkoxides, sulfonyl halides, metalloidal halides,hydrogen halides, and the like. The most preferred Lewis acid catalystsare boron trifluoride etherate complexes, and phosphorus pentafluoride,since excellent results are achieved.

Typical of the Lewis bases which may be employed in the processes ofthis invention when using gaseous monomeric formaldehyde monomer are theorganophosphines, organostibines, organoarsines, primary amines,secondary amines, tertiary amines, the alkali and alkaline earth metalhydroxides, oxides, peroxides, and the like.

Other catalysts which may be employed in association with gaseousformaldehyde and diester monomers in the present polymerizationprocesses are onium salts, metals,

metal alloys, metal carbonyls as well as various oxides, peroxides andhydroxides of the heavy metals.

The types of heterogeneous catalysts may be broadly defined as metaloxides, mixed metal oxides, acid clays, acid treated clays, and ionexchange resins. Acid types of heterogeneous catalysts are used in thepolymerization of trioxane while the basic catalysts are employed in thepolymerization of monomeric formaldehyde. However, acid ion exchangeresins may in some instances be employed in either the copolymerizationof trioxane or monomeric formaldehyde with the diester.

Typical examples of the heterogeneous catalysts are silica alumina,silica magnesia, silica zirconia, alumina boria, alumina magnesia,silica gel, Permutit 8-2 (which is understood to be aluminum silicate),alumina chromia, Amberlite IR (which is understood to be a phenolicmethylene sulfonic cation exchanger produced by the reaction of phenol,formaldehyde and sulfonic acid), montmorillonite, and the like.

Typical examples of the preferred catalysts used when trioxane isemployed in the process of this invention are antimony trifluoride,antimony fluoborate, bismuth trifluoride, bismuth oxyfluoride, nickelousfluoride, aluminum trifluoride, titanium tetrafluoride, manganousfluoride, manganic fluoride, mercuric fluoride, silver fluoride, zincfluoride, ammonium bifluoride, phosphorous pentafluoride, hydrogenfluoride, fluosulfonic acid, antimony chloride, stannous chloride,sodium fluoride, potassium fluoride, lithium fluoride, calcium fluoride,magnesium fluoride, barium fluoride, strontium fluoride, lead fluoride,ferric fluoride, ammonium fluoride, boron trifluoride, aluminum bromide,aluminum chloride, hydrogen chloride, sulfuric acid, and the like.

The amount of catalyst which may be employed in the processes of thisinvention is susceptible to variation. Generally amounts ranging fromabout 0.001 to about 25 percent by weight of the total reaction mass maybe employed. However, the preferred amount of catalyst ranges from 0.01percent to about 2 percent by weight since within this range polymershaving optimum properties such as strength, toughness, and resilienceare obtained. The amount of catalyst employed in the pres ent invention,although not critical, forms an important element of the processes, thusit is desirable to keep the catalyst concentration within the preferredrange outlined hereinabove. The temperature at which the polymerizationprocess is conducted varies with the type of process employed. Thus, inbulk polymerization processes temperatures ranging from about 50 C. upto about C. are employed.

In the solution polymerization processes reaction temperatures may varyfrom about 90 C. up to about 200 C., whereas in vapor polymerizationprocesses temperatures between about -20 C. up to about 200 C. areemployed.

The pressure employed in the polymerization processes of this inventiondepends generally upon the formaldehyde source and catalyst being usedand on the type of process technique being employed. Thus, in solutionpolymerization and vapor polymerization procedures, the pressuregenerally ranges from atmospheric up to about 20 atmospheres. These mildprocess conditions obviate the necessity for expensive, high pressurereaction equipment. In most cases it is preferably to conduct theprocesses of this invention at atmospheric or ambient pres sures.

The processes by which these novel copolymers are produced will befurther understood from the following examples. In all the examples allparts are by weight unless otherwise specified.

EXAMPLES I-V Five copolymerizations are illustrated in Table I employingthe bulk polymerization technique. Diallyl phthalate, diallyl itaconate,dibutyl fumarate, diethyl maleate,

a boiling aqueous solution containing 10 weight percent sodium hydroxidefor 30 minutes.

TABLE IV Caustic degradation for 30 minutes Monomer: Percent retentionDiethyl maleate 94 Dirnethyl fumarate 80 Maleic anhydride 50 TABLEI.-BULK COP'OLYMERIZA'IICEIETTQEFfigRIOXANE \VITH DIHYDROCARBYL Temp.,Percent PMT, 3 Tn 4 Example Monomer PHR 1 Cat. 2 conversion 0. ink

8. 6 0. 115 70 74 175 152 0. 77 8 0. 08 90 10 174 155 0. 38 8 0. 08 7057 179 148 0. 38 0. 12 70 56 181 152 1. 25 Dlallyl maleate- 0. 08 70 58177 158 0. 48

1 PHRParts per hundred of diester monomer. 1 Catalystconcentration-parts per hundred.

8 PMT-polymer melting temperature.

4 Tn-Orystalline melting point.

5 nine-Inherent viscosity as measured in alpha-p-chlorophenol containing2% alpha-pinene at 60 0.

When the above examples are repeated employing esters such as diethylsuccinate, diethyl terephthalate, dibutyl bibenzoate, diethylhomoterephthalate, 2-ethylhexyl terephthalate, dioctadecyl itaconate,and the like, similar results are obtained.

EXAMPLES VI-XlV monomer was 5 weight percent. The following table setsforth the reaction conditions and the results obtained by this solutionpolymerization process.

From the data in Table IV it is noted that the copolymers of thisinvention, i.e., trioxane with diethyl maleate; and trioxane withdimethyl fumarate, exhibit a minimum of loss when compared to a trioxanepolymer containing maleic anhydride.

A third and most rigid test is exhibited by the data in Table V. In thisparticular test, the copolymers of the present invention were firsttreated with an ether solution containing 5 weight percent diphenylamine after which the ether was evaporated. The polymer powder soformedwas then molded into plaques at a temperature of about 190 C. at 10,000p.s.i.g..The same treatment was also accorded a polyoxymethylene polymercontaining succinic anhydride, a composition not contemplated by thepresent invention. The plaques so-obtained were weighed and immersed ina boiling aqueous 10 percent TABLE Ill-SOLUTION POLEYMERIZATION OFTRIOXANE WITH DIHYDROCARBYL STERS IN CYCLOHEXANE Temp., Percent PMT a TnExample Monomer PHR Cat. 2 0. conversion 0. 0. mm

VI Diethyl maleate 5 0. 1 55 60 181-86 161 1. 20 VII- Dibutyl maleate 5O. 1 55 57 1794 3 151 0, 93 VIII- Dibutyl iumarate- 5 0. 1 55 54 179-183158 0. IX.-. Dimethyl i'umarate 5 0. 1 54 180-184 162 1. 20 X Diethylsuccinate 5 0. 1 55 61 184-186 159 1. 13 XL Dimethyl maleate... 5 0. 155 65 185-190 160 0. 91 XIL- Diethyl fumarate 5 0. 1 55 62 181-186160 1. 11 XIII" Dimethyl itaconate 5 0. 1 55 65 179-183 158 0. 96 XIVDimethyl adipate 5 0. 1 55 13 175-180 154 0. 18

1 PH R-Parts per hundred of diester monomer. 1 Catalystconcentration-parts per hundred. a PMT-polymer melting temperature.

4 Tn-Crystalline melting point.

5 mun-Inherent viscosity as measured in alpha-pchlorophenol containing2% alpha-pinene at C.

The novel polymers of the present invention are very resistant tochemical degradation. When these novel polymers are treated with a 10weight percent aqueous sodium hydroxide solution, at a temperaturebetween room temperature and the reflux temperature of the system, fortimes ranging from 1 minute to 5 hours, the net polymer loss experiencedis very slight under these extreme conditions. For example, the polymerof Example I (trioxane diallyl phthalate) was subjected to a 10 weightpercent boiling sodium hydroxide solution for 10 minutes. The results ofthis rigorous test are listed in Table III, and compared to abutyrolactone trioxane copolymer.

TABLE III Comparative caustic degradation Polymer: Percent recoveredDiallyl phthalate 60.6 Butyrolactone 27.8

sodium hydroxide solution for a period of 5 hours. The plaques were thenremoved, thoroughly washed, dried overnight, and reweighed to find thepercentage of weight loss which occurred. The data listed in Table Vdemonstrates the results of this most rigid test.

Inherent viscosity as measured in alpha-p-chlorophenol containing 2%alpha-pinene at 60 C.

3 The succinic anhydride polymer completely disintegrated within 2 hoursafter the initiation of the test, indicating complete thermal andchemical instability.

The plaques obtained from the composition of this invention wereessentially bubble-free, rigid, strong and creasable.

In preparing the copolymers of this invention it is sometimes desirableto first submit the raw copolymer product to a caustic treatment toremove any reactive groups, thereby stabilizing the polymers. Intreating the crude copolymer for commercial utilization it is desirableto use an alkaline solution having a pH of between about 8 and about 14at about room temperature up to about 100 C. for a time ranging fromabout 1 to about minutes. For reasons of economy and time, it isdesirable to contact the crude copolymers of this invention with a 10percent aqueous sodium hydroxide solution. The treated products obtainedby this method are more stable to heat, light, and oxidation.

The strong bases which may be used in this preferred after treatmentinclude alkali and alkaline earth metal hydroxides, oxides, carbonates,acetates, and the like; strong organic bases; ammonia, and the like.Typical of these bases which may be employed are potassium hydroxide,calcium oxide, beryllium hydroxide, magnesium oxide, sodium carbonate,sodium acetate, calcium propionate, ammonia, dimethyl amine, diethylamine, dipropyl amine, dibutyl amine, tetramethyl quanidine, and thelike.

In effecting this after treatment system, other than aqueous alkalinesystems may be employed. Thus, the appropriate strong base may bedissolved in a dimethyl formamide, benzyl alcohol, methanol, anisole,ethylene glycol, or the like. In some instances alkaline solvent systemswhich contain a hydrozyl group such as benzyl alco hol, methanol orethylene glycol, function as the agent of controlled degradation even inthe absence of the above basic substances.

Typical examples of the diester monomers which may be employed in thepresent invention are dimethyl adipate, diethyl adipate, dibutyladipate, didecyl adipate, dioctadecyl adipate, didodecyl adipate,dimethyl azelate, dipropyl azelate, diheptyl azelate, the dimethyl esterof diglycolic acid, the dibutyl ester of diglycolic acid, the dipropylester of diglycolic acid, the dipentadecyl ester of diglycolic acid,dimethyl glutarate, dibutyl glutarate, dipropyl glutarate, dimethylisophthalate, di-2-ethylhexylphthalate, dioctyl pimelate, didodecylpimelate, the diethyl ester of pinic acid, the dipropyl ester of pinicacid, the dipropyl ester of suberic acid, the diisopropyl ester ofsuberic acid, di-tbutyl sebacate, the dimethyl ester of acetylenecarboxylic acid, the diethyl ester of acetylene dicarboxylic acid, themethyl ethyl ester of acetylene vdicarboxylic acid, the dioctadecylester of acetylene carboxylic acid, the dipropyl ester ofalpha,alpha-diethyl adipic acid, the dimethyl ester of linoleic aciddimer, the dipropyl ester of cyclohexane dicarboxylic acid, diethylterephthalate, dibutyl terephthalate, dipropyl phthalate, dioctadecylhomoterephthalate, dimethyl bibenzoate, diallyl bibenzoate, methylcyclohexyl maleate, didodecyl mesaconate, didodecyl citraconate, o-tolyloctadecyl itaconate, diisopropyl maleate, dioctadecyl maleate,dipentadecyl maleate, didodecyl maleate, diisoamyl fumarate,di-Z-ethylhexyl fumarate, octylethyl fumarate, bis-o-tolyl fumarate,diisopropyl itaconate, didodecyl itaconate, bis-dotriacontyl itaconate,diheptyl itaconate, and the like.

Typical of the Lewis acid catalysts which may be employed in the processof this invention are antimony trifluoride, antimony fiuoborate, bismuthfluoride, bismuth oxyfluoride, nickelous fluoride, aluminum trifluoride,titanium tetrafluoride, manganous fluoride, manganic fluoride, mercuricfluoride, silver fluoride, zinc fluoride, ammonium bifluoride,phosphorus pentafluoride, hydrogen fluoride, fluosulfonic acid, antimonychloride, stannous chloride, sodium fluoride, potassium fluoride,lithium fluoride, calcium fluoride, magnesium fluoride, barium fluoride,strontium fluoride, lead fluoride, ferric fluoride, ammonium fluoride,thionyl chloride, phosphorus trichloride, aluminum chloride, aluminumbromide, stannic chloride, titanium tetrachloride, zirconium chloride,boron trifluoride diethyl etherate complex, boron trifluoride 10 dibutyletherate complex, boron fluoride complexes of aryl amines such asaniline, alpha-naphthyl amine, betanaphthyl amine, diphenyl amine andbenzidine, boron trifluoride complexes of pyridine, phenothiazine,glycine, alpha-alanine, semicarbazide, urea, and the like.

Typical examples of Lewis base catalysts which may be employed in theprocess of this invention are triphenyl phosphine, tritolyl phosphine,trixylyl phosphine, trinapthyl arsine, tributyl phosphine, triethylstibine, dimethyl phenyl arsine, tricyclohexyl phosphine, methyl dioctylstibine, dixylyl ethyl arsine, trimethyl amine, triethyl amine, trihexylamine, diethyl amine, di-N-propyl amine, dioctyl amine, cyclohexylamine, dicyclohexyl amine, piperidine, N-ethyl piperidine, morpholine,N- methyl morpholine, pyrrolidine, N-ethyl pyrrolidine, butyl lithium,sodium cyanide, cesium hydroxide, strontium hydroxide, rubidiumhydroxide, sodium hydroxide, potassium hydroxide, lithium hydroxide,barium hydroxide, calcium hydroxide, sodium oxide, sodium peroxide,barium peroxide, and the like.

Typical examples of oniumsalts which may be employed as catalysts aretrimethyl stearyl ammonium laurate, tetra-N-butyl ammonium laurate,triethyl benzyl ammonium laurate, benzyl trimethyl ammoniumnonylphenolate, dimethyl diammonium acetate, dimethyl diammonium benzoate,dimethyl dioctadecyl ammonium acetate, N,N-diethyl piperidiniumchloride, tetra-N-butyl ammonium iodide, N-phenyl ethyl tetramethyleneammonium iodide, dibutyl octadecamethylene ammonium acetate, bis-(tri-N-butyl ammonium iodide)propane, betaine methyl ester ofN-methyl-N-phenyl glycine, l-(carboxy methyl) pyridinium betaine,(carboxy methyl) tridecyl ammonium chloride, triethyl octadecylphosphonium bromide, tetraethyl phosphonium iodide, tributyl ethylphosphonium iodide, phenyl ethyl pentamethyl phosphonium acetate,bis-(triethyl phosphonium acetate)butane, tributyl sulfonium bromide,trimethyl sulfonium iodide, phenyl dibutyl sulfonium acetate, cyclohexyldiethoxy sulfonium benzoate, and the like.

Metal alloy catalysts which may be employed in the process of thisinvention are alloys of aluminum with copper, silver, gold, beryllium,magnesium, calcium, strontium, barium, zinc, cadmium, mercury, silicon,titanium, zirconium, germanium, tin, lead, vanadium, niobium, tantalum,antimony, bismuth, chromium, molybdenum, tungsten, manganese, iron, andnickel. Specific alloys which have been satisfactory in the past arealuminum magnesium alloys, aluminum cobalt alloys, aluminum copperalloys, aluminum copper manganese alloys, aluminum silicon alloys,aluminum zinc alloys, aluminum magnesium titanium alloys, and alloyscontaining aluminum, cadmium, zinc, calcium and lithium as well asamalgams of all of the alloys listed hereinabove.

Typical of the organometallic compounds which may be used as catalystsin the process of this invention are phenyl lithium, methoxyphenylsodium, decoxy sodium, copper mercaptide, copper abietate, coppersteal'ate, methyl magnesium iodide, phenyl magnesium bromide, diethoxymagnesium, calcium hydride, dimethyl cadmium, diphenyl mercury, calciumisopropoxide, aluminum stearate, tetraisopropyl titanate, diphenyl tin,triphenyl bismuth, dicyclopentadienyl iron, triethyl aluminum, trimethylaluminum, tri-N-butyl aluminum, triisopropyl aluminum, cobalt carbonyl,iron carbonyl, nickel carbonyl, and the like.

Typical of the heterogeneous mixtures of catalysts which may be employedin the process of this invention are silica alumina, Amberlite IR (acidform) as described hereinbefore, montmorillonite (mixture of silicaalumina and magnesia), silica gel, Permutit S-2 (basic form) as described hereinbefore, alumina chromia, silica magnesia, silica boria,silica zirconia, alumina boria, as Well as other metal oxides, mixedmetal oxides and ion exchange resins.

Other forms of heterogeneous catalysts which may be used in the processof this invention are disclosed in Ion 11 Exchange Technology, AcademicPress, New York (1956); Ion Exchange Resins, by Kunin and Myers, JohnWiley and Sons (1950); and Dowex Ion Exchange, The Dow Chemical Company(1958).

Although the polymers of this invention have improved resistance tochemical and physical degradation, nevertheless for some uses it may bedesirable to make use of previously known stabilization techniques inorder to effect still further improvement in stability. The techniqueswhich may be so used are in general those procedures which haveheretofore been successfully used with hitherto known polyformaldehydepolymers and copolymers. Therefore stabilizer additives may becompounded with the novel polymers of this invention. Typical of thesestabilizer additives are hydrazines (U.S. 2,810,708); hydrazones(Belgian 597,962); phenols (U.S. 2,871,220); ureas and thioureas (U.S.2,893,972); sulfides and polysulfides (Belgian 599,409); amines (U.S.2,920,059 and 2,936,- 298) oxalic diamides (Belgian 584,257);polysulfonic acids (Belgian 585,164); hydroxy anthroquinone (Belgian585,165); benzophenones (Australian 230,163) and polyamides (U.S.3,001,966). These stabilizers may be compounded with the novelinterpolymers of this invention after the polymerization reaction hasbeen completed.

Other antioxidants such as the o-substituted phenols may be compoundedwith novel comonomers of this invention. Typical examples of theseantioxidants are 4,4'thiobis (2,6-di-tert-butylphenol) 4,4'-thiobis(Z-methyl-6-isopropylphenol 4,4'-thiobis (2-ethyl-6-sec-butylphenol)4,4'-thiobis (2,6-diisopropylphenol) 4,4'-thiobis-(2-methyl-6-tert-butylphenol) 4,4'-thiobis(2-n-butoxy-6-tert-butylphenol)4,4'-thiobis(2-methoxy-6-sec-butylphenol), 4,4'-dithiobis-(2-n-propyl-6-tert-butylphenol 4,4'-trithiobis 2-methyl-6-tert-butylphenol) 2,2-thiobis (4-methyl-6-tert-butylphenol)2,6-di-tert-butylphenol,

4,4'-methylene bis(2,6-dimethylphenol), 4,4'-methylenebis(2,6-di-tert-butylphenol), 4,4'-methylene bis (2,6-diisopropylphenol)4,4-methylene bis(2,6-di-sec-butylphenol) 4,4'-methylene bis[2-sec-butyl-6- (2-hexyl) phenol] and the like, as well as combinationsof these.

Similarly the interpolymers may be end capped in lieu of the preferredcaustic after treatment step, by reacting the terminal hydroxyl groupsof the copolymer with an anhydride such as acetic anhydride (U.S.2,964,500); or a dialkyl acetal (Belgian 570,884); to esterify thegroups.

The polymers may also be subjected to a combination of the compoundingof stabilizers and end capping. Thus, one may end cap the crude polymerby reacting the polymer with an anhydride and thereafter compoundstabilizers such a hydrazines, phenols, ureas, and the like, with thepolymer product.

Another technique by which additional stabilization may be achieved isto rigorously remove catalyst residues from the novel polymers of thisinvention. Thereupon, if desired, a stabilizer additive or end cappingprocedure, or both, may beutilized.

A still different combination which may be used to further stabilize theinterpolymers involves caustic treatment followed by addition ofstabilizers. Any of the stabilizers referred to hereinabove may beemployed subsequent to the preferred caustic after treatment step. Thiscombination of caustic after treatment and subsequent addition ofstabilizers is the most preferred method of giving additionalstabilization to the interpolymers of this invention.

In all cases where a stabilizer additive is used, it is compounded withthe interpolymer in a proportion of between about 0.003 and 15 percentby weight, based on the weight of the polymer. It should be noted thatthe stabilizers may, in some instances, be added prior to the causticdegradation step. However, it is preferred in most instances to add thestabilizers after the caustic degradation step since a polymer isobtained via this method which is more resistant to thermal degradationand oxidative deterioration.

The copolymers of this invention are useful for the preparation of films(as disclosed in US. 2,952,878), sheets, funicular structures such asfibers, filaments, bristles, rods, tubes and molding powders. Thus, thecopolymers of this invention may be employed in any general use forwhich known tough and thermally stable thermoplastic polymers have beenput.

Typical methods of molding the interpolymers of this invention are thosetechniques set forth in Polymer Processes, vol. X, High Polymers bySchildknecht, Interscience Publishers, New York (1961). Typical of thedescribed techniques at page 688 are compression molding, jet molding,transfer molding, injection molding, extrusion, etc.

Having thus described this unique invention and its embodiments, it isnot intended that this invention be limited except as set forth in thefollowing claims.

I claim:

1. The process of preparing a linear thermoplastic oxymethylenecopolymer comprising the step of copolymerizing (a) a formaldehydeselected from the group consisting of essentially anhydrous monomericformaldehyde and essentially anhydrous trioxane, and

(b) a diester of a dicarboxylic acid, said diester having the formula:

wherein R and R are monovalent hydrocarbyl groups having up to about 32carbon atoms; R is a divalent hydrocarbyl radical having from 1 to about12 carbon atoms; the amount of said diester chemically combined in saidpolymer ranging from about 0.1 to about 20 percent by weight of saidpolymer; said polymer having a polymer melting temperature of from aboutC. to about C. and an inherent viscosity of from about 0.3 to about 5.0determined by measurement of 0.5 percent by weight of polymer inp-chlorophenol containing 2 percent alpha-pinene at 60 C.; saidcopolymerization step being conducted under an essentially anhydrousinert atmosphere in an inert solvent and in the presence of from about0.001 to about 25 percent by weight, based on the total weight of thereactants, of a polymerization catalyst, at a temperature between about-90 C. and about 200 (2., and at a pressure of from about atmospheric upto about 20 atmospheres.

2. The process of claim 1 wherein said formaldehyde is essentiallyanhydrous monomericformaldehyde.

3. The process of claim 1 wherein said formaldehyde is essentiallyanhydrous trioxa'ne and said catalyst is a Lewis acid catalyst.

4. The process of claim 1 wherein said diester is diethyl maleate.

5. The process of claim 1 wherein said diester is dimethyl fumarate.

6. The process of preparing a linear thermoplastic oxymethylenecopolymer comprising the step of copolymerizing (a) a formaldehydeselected from the group consisting of essentially anhydrous monomericformaldehyde and essentially anhydrous trioxane, and

(b) a diester of a dicarboxylic acid, said diester having the formula:

0 0 IMO-(l-R--OR: wherein each of R and R is selected from the groupconsisting of alkyl, cycloalkyl, and alkaryl radicals,

13 14 each radical containing up to about 32 carbon atoms; 8. Theprocess of claim 6 wherein said formaldehyde R is selected from thegroup consisting of alkylene, is essentially anhydrous trioxane and saidcatalyst is a arylene, and cycloalkylene radicals, each radical hav-Lewis acid catalyst. ing up to about 12 carbon atoms; the amount of saiddiester chemically combined in said polymer rang- 5 References Cited ingfrom about 0.1 to about 20 percent by weight UNITED STATES PATENTS ofsaid polymer; saidpolymer having a polymer melt- 2,488,883 11/1949Shokal et a1.

ing temperature of from about 140 C. to about 190 C., and an inherentviscosity of from about g gi 0.3 to about 5.0 determined by measurementof 0.5 10 3123578 3/1964 Kragt percent by weight of polymer inp-chlorophenol con- 3 219 630 11/1965 taining 2-percent alpha-pinene at60 C., said copolymerization step being conducted under an essential-3296210 1/1967 wllson et 260.43 1y anhydrous inert atmosphere in aninert solvent and FOREIGN PATENTS in the presence of from about 0.001 toabout 25 per- 5 699,648 11/1953 Great Britain cent by weight, based onthe total weight of the reactants, of a polymerization catalyst, at atempera- WILLIAM H. SHORT, Primary Examiner ture between about 90 C. andabout 200 C. and at a pressure of about atmospheric up to about 20 QUASTAssistant Exammer atmospheres. 20

7. The process of claim 6 wherein said formaldehyde US is essentiallyanhydrous monomeric formaldehyde. 7, 45.9, 45.95, 67

